This spectacular video of three jets passing at high altitude was taken by Captain Neil Morrison. Captain Morrison's jet was a 38,000ft, the aircraft coming towards him at 39,000 and the one above travelling in the same direction at 40,000ft. SEE World renowned 747 pilot reveals his best ten pictures Separations of just 1000ft are standard today for suitably equipped jets with the sophistication of autopilots and cockpit automation as well as satellites.   https://www.facebook.com/neilemorrison/videos/2029325727101140/?t=2 Suitability equipped jets are described as Reduced Vertical Separation Minima (RVSM). Within RVSMairspace (between FL290 and FL410 inclusive) the vertical separation minimum is:

• 1000ft (300m) between RVSM-approved aircraft, and
• 2000ft (600m) between non-RVSM approved state aircraft and any other aircraft operating within RVSM airspace.
• 2000ft (600m) between non-RVSM aircraft operating as general air traffic (GAT) and any other aircraft within RVSM airspace.